Des Moines Register: Polk County could have a response to one of the biggest criticisms farmers face with Iowa’s voluntary approach to improving water quality: that they’re too slow to adopt conservation practices that can curb runoff into the state’s rivers, streams and lakes. The county is leading a local, state and federal partnership to rapidly build saturated buffers and bioreactors — 51 this year alone, and 150 the following year. The structures are one of the most effective ways that farmers can curb runoff of nitrogen and, to a lesser extent, phosphorus into Iowa’s waters. A saturated buffer not only cleans surface water, as a typical grass buffer would, but filters runoff that flows underground.